8x(x+y)-x-y=(8x-1)(x+y)
x^3 - x= x(x^2 -1)
81x^2y^2 -25= (9xy)^2 -5^2 = (9xy-5)(9xy+5)
27x^3 -1 = (3x)^3 -1 = (3x-1)(9x+3x+1)
\(81x^2y^2-25=\left(9xy-5\right)\left(9xy+5\right)\)
\(x^3-x=x\left(x-1\right)\left(x+1\right)\)
\(8x\left(x+y\right)-x-y=\left(x+y\right)\left(8x-1\right)\)